1. Field of Invention
The present invention relates to a fuel for internal combustion-powered tools, especially for setting tools for fastening elements, such as gas-powered nail-driving tools, and based on a liquefied, combustible gas or gas mixture with a vapor pressure from about 2 to 15 bar absolute at 20° C.
2. Description of the Prior Art
Internal combustion-powered tools of the type described above, namely, setting tools for fastening elements, are known, for example, from German publication DE-A-40 32 202. With the help of these tools, fastening elements, such as nails, bolts, etc., can be driven directly, under the action of the power of combustion of the combusted fuel, normally a liquefied, inflammable gas or gas mixture, into materials, such as wood, steel, concrete and the like, to which a fastening element is to be fastened.
Internal combustion-powered tools of this type include, for example, a combustion chamber and a piston, which can be moved in a piston guide and is acted upon by the expanding combustion gasses produced in the combustion chamber. By igniting the mixture of air and fuel filling the combustion chamber, the piston is moved away from the combustion chamber, strikes the fastening element and drives it into the material. The energy gained by the combustion of the fuel depends to a large degree on the rate of combustion, which, in turn, depends on the fuel to air ratio.
In conventional, internal combustion-powered tools of this type, a mixture of, for example, methylacetylene and propadiene or a mixture of propane, butane, propene or ethane is used as fuel. For conventional, commercial, internal combustion-powered tools of this type, especially mixtures of methyl acetylene, propadiene, propene and/or butane are used, which are also known under the name of MAPP. Such gas mixtures are obtained as waste products when coking low-grade anthracite and provide a relatively high combustion speed, which is important if the tools are to have a high efficiency.
However, these conventional fuels have a series of disadvantages. For example, the commonly used MAPP mixtures generally contain small amounts of butadiene, which is poisonous and permissible only in amounts of less than 0.1% by weight. Pure, butadiene-free MAPP gases are difficult to obtain and expensive. Conventional mixtures of hydrocarbons or pure hydrocarbon gases, such as butane or propane, burn more slowly and are not suitable for the present application.
In particular, most of the known gas mixtures, used as fuels, evaporate slowly and weakly at low temperatures (−5° C.). This is a problem for the tools in question, which must also be usable on building sites even at temperatures below 0° C.
On the other hand, hydrocarbons, which evaporate quickly and almost completely at low temperatures, are obtainable only at great expense and frequently have excessively high vapor pressures, which make it difficult to adhere to government regulations concerning the handling of liquid gas mixtures of this type. For example, the aerosol regulations require that the pressure of the liquefied gas mixture at 50° C. does not exceed 12 bar above atmospheric pressure.
If one attempts to solve the problems of conventional fuels at low temperatures by adding a larger amount of fuel to the combustion chamber and, with that, using a fatter mixture, problems arise at high temperatures (for example, at 50° C.) in the combustion space, so that it is more difficult to control the combustion energy, which is to be used, and, with that, the driving-in energy of the fastening element.
An object of the present invention is to provide a fuel for internal combustion-powered tools of the type under discussion, which not only is composed of components, which are safe form a health point of view, but also can be produced inexpensively.
Another object of the present invention is to provide a fuel for internal combustion tools and having an improved cold temperature behavior and, if necessary, an improved warm temperature behavior.